// Copyright 2023 The Abseil Authors.

//

// Licensed under the Apache License, Version 2.0 (the "License");

// you may not use this file except in compliance with the License.

// You may obtain a copy of the License at

//

//      https://www.apache.org/licenses/LICENSE-2.0

//

// Unless required by applicable law or agreed to in writing, software

// distributed under the License is distributed on an "AS IS" BASIS,

// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

// See the License for the specific language governing permissions and

// limitations under the License.

//

#ifndef ABSL_SYNCHRONIZATION_INTERNAL_FUTEX_WAITER_H_

#define ABSL_SYNCHRONIZATION_INTERNAL_FUTEX_WAITER_H_

#include <atomic>

#include <cstdint>

#include "absl/base/config.h"

#include "absl/synchronization/internal/kernel_timeout.h"

#include "absl/synchronization/internal/futex.h"

#include "absl/synchronization/internal/waiter_base.h"

#ifdef ABSL_INTERNAL_HAVE_FUTEX

namespace absl {

ABSL_NAMESPACE_BEGIN

namespace synchronization_internal {

#define ABSL_INTERNAL_HAVE_FUTEX_WAITER 1

class FutexWaiter : public WaiterCrtp<FutexWaiter> {

 public:

  FutexWaiter() : futex_(0) {}

  bool Wait(KernelTimeout t);

  void Post();

  void Poke();

  static constexpr char kName[] = "FutexWaiter";

 private:

  // Atomically check that `*v == val`, and if it is, then sleep until the

  // timeout `t` has been reached, or until woken by `Wake()`.

  static int WaitUntil(std::atomic<int32_t>* v, int32_t val,

                       KernelTimeout t);

  // Futexes are defined by specification to be 32-bits.

  // Thus std::atomic<int32_t> must be just an int32_t with lockfree methods.

  std::atomic<int32_t> futex_;

  static_assert(sizeof(int32_t) == sizeof(futex_), "Wrong size for futex");

};

}  // namespace synchronization_internal

ABSL_NAMESPACE_END

}  // namespace absl

#endif  // ABSL_INTERNAL_HAVE_FUTEX

#endif  // ABSL_SYNCHRONIZATION_INTERNAL_FUTEX_WAITER_H_